Guide wires are used to insert and guide a catheter to a target site for use in treatment of cites at which open surgery is difficult or which require low invasiveness to the body or in examination or treatment of a cardiac disease through cardioangiography or the like.
For example, in the process of PCI (Percutaneous Coronary Intervention), a treatment is conducted as follows. The distal end (tip) of a guide wire protruding from the distal end of a balloon catheter is inserted together with the balloon catheter to a position immediately on the proximal side of a stenosed portion of the coronary artery, which portion is the target site, under fluoroscopic observation. Next, the distal end of the guide wire is passed through the stenosed portion. Thereafter, the balloon of the balloon catheter is guided to the stenosed portion while still positioned along the guide wire, and the balloon is expanded to dilate the stenosed portion, thereby recovering a quantity of bloodstream flow.
For instance, in order to insert a guide wire from a femoral artery and advance it through an aorta, an aortic arch and a coronary artery orifice into the coronary artery by the Seldinger technique, it is desirable that the guide wire be excellent in flexibility for following the blood vessels (trackability) and in pushability which ensures effective transmission of a pushing force from the operator's hand (the proximal side) to the distal part of the guide wire.
In addition, for the purpose of advancing the guide wire into a desired branch at a branching part of the coronary artery or the like, a distal part of the guide wire may in some cases be shaped in conformity with the shape of the branching part. Such a shaping operation is ordinarily performed with the surgeon's fingers at the time of surgery, and is called “reshaping”.
Especially in the case of inserting the distal end of a guide wire into the coronary artery on the peripheral side, it may in many cases be impossible to select the desired branch while using the angle- or J-type tip shape of the guide wire preformed according to the known art, and the guide wire tip may be reshaped into a desired shape and then inserted again. When the shape of the guide wire tip is not satisfactory for the intended selection of the desired branch, it is necessary to withdraw the guide wire from the catheter, reshape the guide wire tip again and then insert the guide wire once again.
There is also known a guide wire in which a wire body is composed of a Ni—Ti alloy exhibiting superelasticity, for obtaining flexibility at the distal part of the guide wire. In this case, however, the superelasticity of the distal part of the wire body makes the reshaping difficult. In view of this, there has been developed a guide wire having a reshapeable distal part.
A guide wire in which a distal part of a core wire (wire body) composed of a superelastic alloy has had its superelasticity degraded by heat treatment is disclosed in, for example, U.S. Pat. No. 5,452,726.
However, in the case where the superelasticity of the distal part is degraded by heat treatment, the distal part provided easily with a new shape upon reshaping may return to its original shape by losing the new shape upon being inserted into a living body. This is because the superelastic alloy tends to return to its original straight shape due to its own shape memory effect. More specifically, the heat treatment raises the transformation temperature of the distal part, and the heat-treated part does not exhibit superelasticity at room temperature, so that this part can be shaped as if it were plastically deformed. However, the deformation in this instance is an apparent plastic deformation. Therefore, when the reshaped part is inserted into the living body and is warmed up to the body temperature, its transformation temperature is approached and it returns to the original straight shape.
Proposals have also been made for a guide wire in which the superelasticity of the distal part of a core wire (wire body) is deprived by cold drawing. An example is described in U.S. Pat. No. 5,238,004.
However, in the case where superelasticity is lost by cold drawing, the effect may often be unsatisfactory and so reshaping may be difficult to achieve. In addition, the worked part may become harder than required, thereby lowering the flexibility of the distal part of the guide wire. In order to enhance the flexibility, it may be contemplated to set a flat plate-like section (reshapeable section) to be thinner. In that case, however, the strength of the flat plate-like section cannot be maintained. Since the guide wire tip may be advanced through a stenosed portion while being rotated or may be pulled in a bent state, it must have a strength (e.g., tensile strength) not lower than a certain value. Therefore, there is a limit to the thinning of the flat plate-like section. Accordingly, by this approach it is quite difficult, if not impossible, to secure both flexibility and strength.